British light-heavyweight Buatsi made a winning yet unimpressive debut to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a split decision in a close 10-round bout at the Manchester venue.
But the challenger found success, landing some telling individual punches in a contest where the approaches never quite clicked, with excessive holding disrupting the fight.
Two judges scored it 96-94 in favor to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best performance but how do champions respond? They succeed," Buatsi said in the ring as he was greeted with disapproval from the crowd.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in February - to earn a 20th career victory.
Some ringside observers thought the challenger, 31, should have been awarded the victory but the contender experienced the second setback of his 28-bout professional journey.
Buatsi Secures Win in Slow Match
The fighter's advancement has stalled in recent years through management issues and extended periods of lack of fights.
Once tipped as the rising talent of British boxing, he now is positioned trying to fulfil that early promise - possibly in what appears to be a last chance - under fresh management.
He began cautiously, with the two boxers prepared to overcommit in a tentative early stages.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in 2022 after breaking his hand mid-fight, was making just his second bout at light heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for Buatsi, who operated with a protective stance to edge the better stanzas.
The audience's tolerance diminished because of regular grabbing, with the challenger slipping to the canvas various instances during close exchanges.
The underdog ended stronger, but multiple periods were challenging to assess. Although, previous titleholder the boxing analyst - working with Dazn - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the presence of hard hitter Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Memorial Motivates All-Manchester Contest
In the secondary fight, Lyndon Arthur beat Bradley Rea by close verdict in a excellent Manchester vs Manchester fight to secure the European light-heavyweight title.
The stadium grew hushed for a profoundly moving tribute before the fight as 10 bells rang in memory of local hero Hatton, who died at age 46 in last month.
It was the premier televised fight night in the location since Hatton's passing. As the final chime ended, the quiet transitioned to a shout of "only one Ricky Hatton".
The competition during the bout reflected the sentiment. Arthur was floored by a significant blow squarely on the chin in the second round, rising shakily to his footing on the count of eight.
But the traditional red attire of Arthur soon pressed ahead again. From the other corner, the opponent - in rival City blue - was damaged soon, noticeable damage appearing under his face as the pair exchanged punishing blows.
The challenger, 27, landed power punches but Arthur, thirty-four, responded in kind with stinging uppercuts as the pace hardly diminished over the full distance.
The victor edged the result with official scores of even score, close margin and wider gap, but the two athletes were relentless and courageous, all the qualities their hero Hatton embodied.
